- How does 3D printing work?
- Why 3D printing though?
- What 3D printing methods are there?
- Vat Polymerization technologies
- Powder Bed Fusion technologies
- Other technologies and printing methods
If you google 3D printing or additive manufacturing (AM), you’d find it defined as: “it is a process that creates a physical object from a digital design”. If you stop and think about it for a moment, you quickly realize that there are is an abundance of physical objects that exist today which were made from digital designs. Could your sweater be 3D printed? What about those glamorous cakes sold in stores? The answer, it seems, is in the details.
How does 3D printing work?
Currently, there are many different technologies of 3D printing, but what they all have in common is that they build objects layer-by-layer according to the code they receive. This code, which forms the blueprints of an object, contains a set of coordinates for a machine to follow to form material together to create the object - similar to how you would play Connect the Dots to create a picture on a piece of paper. However, before you have a code, you have the digital file or Computer-Aided Design (CAD) file. Programs called slicers analyze the file and generate a code by slicing an object into thin layers and applying the settings for the 3D printing process.
Why 3D printing though?
Before the invention of 3D printers back in 1980, we’d already been producing a wide variety of objects using other machines and processes. So, you may be asking why was 3D printing introduced? Many production methods are based on subtractive manufacturing – “the large family of machining processes with material removal as their common theme”. 3D printing, on the other hand, operates on the opposite end of the spectrum by building an object from scratch. This leads to the efficient use of resources by minimizing waste and time spend, as well as opening a world of possibilities that would otherwise be impossible with traditional manufacturing methods. The trick to it all is being able to understand which method you should use and when.
What 3D printing methods are there?
Despite the fact that the concept behind 3D printers is the same, the different technologies and materials available have a huge influence on the kinds of possibilities and specifications that each method brings to the table.
Fused Deposed Modeling/ Fused Filament Fabrication (FDM/FFF)
FDM would have to be the most well-known 3D printing technology on the market. It works similar to a glue gun or cream injector (depending on which one you use more). FDM machines use strings of solid material which they melt inside a heated nozzle to form an object. Starting from the bottom of an object, FDM printers deposit layers of melted material on one another according to the coordinates received in the code. The extruded plastic cools and becomes solid quite quickly, so the machine can continue uninterrupted and place a new layer on top of the previous somewhat hardened layers.
- Advantages: Desktop FDM printers and their filaments are extremely affordable; come in a wide variety of materials and colors; easy working principle; some 3D printers allow owners to perform multiple upgrades.
- Disadvantages: Most affordable FDM printers come with a degree of inaccuracy; the laws of gravity prevent objects to be printed with big overhanging without any supports under them; objects without a flat surface to start with are harder to print; layers are fairly visible on the surface.
- Interesting fact: The range of FDM printers is huge, with desktop printers that can be purchased for as little as $100 to industrial grade printers that can fetch up to $14,000.
Industrial FDM Printers
It can be difficult to differentiate between a desktop and industrial FDM printer, especially in the case of hybrid printers. The biggest difference is the quality or resolution that they’re capable of producing. In addition to this are the specs which include size, hardware, software, frame material, sensors and other features.
Upgraded FDM printers
Due to the easy working principle of FDM printers, numerous upgrades and reworks are possible which can take the technology to a whole new level. Did you know there are FDM printers out there which can produce objects from concrete, metal, wood composites and food such as chocolate, cheese, meats and vegetables.
Dual-nozzle and multi-material FDM printers
Typically, FDM printers have only one nozzle which extrudes the filament. However, some of them are capable of adding multiple nozzles to print several different strings at the same time. As a result, they are capable of using different materials in the same run – for example, adding a dissolvable support structure that is easy to remove. This is how dual-nozzle FDM printers overcome some geometrical limitations such as overhangs and make hollow objects and elements easier to print and cleanout. There are also different types of multi-material upgrades that enable the use of several colors at the same time to create colorful objects.
Vat Polymerization technologies
Some 3D printing technologies like stereolithography (SLA) use polymerization processes to create an object from a Photoresist liquid material. Polymerization had already been used for other manufacturing and personal processes – for example, creating stamps, dentures, PCBs or even gel manicure. The key is in the photoresist material (photopolymer), essentially it’s a liquid resin that solidifies due to its reaction under a light source such as LEDs, lasers, UV lamps, etc.
Digital Light Processing (DLP)
These 3D printers make objects upside down by immersing the build platform into a resin tank and lighting the areas from underneath which results in materials becoming solid layer-by-layer. They use a code to coordinate the light source and polymerize only the areas that make up an object. After the first layer is formed, the platform ascends to let the uncured resin fill the tank and the process begins once again until the whole object is created. As a light source, DLP printers use projectors or LEDs to solidify the resin. This digital screen under the tank displays the image of each layer, built from square pixels like in old computer games. Thanks to this, a layer of an object is formed from small rectangular bricks called voxels. DLP machines can be covered with a toned glass/plastic to prevent outside lighting such as the sun and lamps from reacting with the resin. After an object is finished, it also needs to be cleaned from left-over liquid and cured under a UV light or natural sunlight to solidify better.
SLA printers work almost the same as DLP machines but source their light from lasers. Generally, the laser inside the machine transmits a light to the galvanometer or a deflection mirror which is in motion. Their role is to aim the laser beam in accordance with the code to the specific areas on a print bed that need to become solid. Lasers can create smooth rounded lines and be more precise lighting the material, so good SLA machines (even desktop ones) have higher resolution and smoother surface of prints than DLP printers. However, LEDs can illuminate resin in several points at the same time whereas a laser beam needs to travel around the whole contour of the object. SLA printers can cure resin through the translucent bottom of the tank like DLP but also from the top of a bath with material. In the latter, the build platform isn’t lifting up but rather, slightly going down while a roller moves across the build chamber to smooth out the solidified layer and bring more uncured resin to the printing area.
Continuous Liquid Interphase Printing (CLIP)
This technology is also another type of DLP printing but an improved one for increasing the working speed. CLIP printers also use projectors as a light source but instead of lifting the platform up after every single layer created, they continuously lighten photopolymer. To make such production possible, these machines have an oxygen-permeable membrane which lies below the resin and creates a “dead zone” of uncured photopolymer. Thanks to this, CLIP printing is usually much faster than SLA while maintaining a high resolution for detailed parts.
Desktop and Industrial Polymerization printers
Unlike FDM technology, polymerization is a more complicated process that requires bigger expenses, simply because strong and precise light sources and photopolymers cost much more than plastic and heating tools.
Good news: Some companies and enthusiasts managed to invent cheaper models of desktop DLP printers with good quality – some of them can be purchased for under $400.
Bad news: Photopolymers are still quite expensive – about $70-80 per liter is considered a good deal if you compare it to resin for high-end machines that can cost up to $200 a liter.
Despite the fact that polymerization technologies are capable of high detail, some low-end DLP machines with weak light sources or poor-quality photopolymers are still capable of producing bad results - poor details, cracks and fragile parts. It also becomes hard to defy professional and amateur machines, especially because of the growing interest in SLA and DLP printing. Some desktop machines like the ones made by Formlabs are widely used by professionals like dentists and jewelers despite their size and affordable price of $3,499. Yes, that is considered affordable when compared to the Carbon M2 (CLIP) printer which costs $50,000 per year (three-year minimum) plus $10,000 installation and training fees over $14,000 for accessories package.
- Advantages of SLA/DLP/CLIP printing: Better details; high resolution; don’t need a flat surface to start with; smoother surface; there are some resin types that facilitate the making of models for metal casting, ISO certified resins for creating medical tools and devices
- Disadvantages: Printers and materials are expensive; less materials and colors to choose from compared to FDM; some SLA printers are really slow; thanks to gravity heavy and complex objects still require supports to “hang on” if a build platform lifts up
Powder Bed Fusion technologies (SLS, DMLS, SLM, EBM, CJP, MJP, MJF)
If you enjoy building sandcastles on a beach then you would probably like the next group of 3D printers. Powder Bed Fusion is a 3D printing technology group which works with powdered materials like gypsum, sandstone, metal alloys, nylons and others. The idea is also quite simple: these powdered materials are melted or sintered layer-by-layer at the positions where the object needs to exist. Melted or sintered powder becomes solid, so after a single layer is done, the platform goes down and a roller spreads new powder across the area.
Selective Laser Sintering (SLS)
SLS technology is a great example of the powder bed fusion method. It works with monochrome powdered materials like nylon (polyamide), ceramics, glass and its many variations. Currently, there are a large number of materials with different properties including durable, strong, and biocompatible. Despite SLS printers come in a desktop version, this technology is commonly used in industrial manufacturing with large build volumes. As a main tool, these printers use a high-powered laser to sinter the powder. After all the layers are completed, a specialist removes the unused powder and cleans parts just like an archeologist cleans a site that contains dinosaur bones.
- Advantages: SLS printers can produce very complicated parts and they don’t need supports at all; great mechanical properties of prints; good chemical resistance
- Disadvantages: Prints are porous and require sealing; hollow but fully enclosed parts are impossible to print because the un-sintered powder would stay inside a part; prints require thermal treatment after being produced
Direct Metal Laser Sintering (DMLS)
Although this technology is a variation of SLS, the working principle is the same. The main difference being that DMLS printers work with powdered metal alloys that allows the production of metal parts from stainless steel, maraging steel, cobalt chromium, inconel, aluminum, and titanium. Of course, metals are harder to melt, so the surface of a part printed on DMLS machine can be rough. These parts usually require post processing: machining or laser polishing to improve the final appearance. However, the geometrical possibilities and the production speed make the DMLS process a strong competitor to other methods in aerospace, medical, prototyping, and tooling spheres.
Selective Laser Melting (SLM)
SLM technology is a close relative of DMLS and SLS but rather than the laser sintering the metal powder, it melts it. So, as DMLS printers heat the powder up for the grains to fuse together, SLM machines melt them to become a liquid and solidify together completely. This leads to the parts coming out stronger and less porous.
- Advantages: Creates stronger parts; smoother surface
- Disadvantages: Can work with single metal powders only
Electron Beam Melting (EBM)
One more technology, which can work with metal powders, is EBM. Like SLM, EBM printers melt the powder into a solid piece. The difference is that instead of a laser inside they use an electron beam (controlled by a computer) to heat and melt the material. EBM printing is performed in a vacuum and can reach temperatures of up to 1832 degrees Fahrenheit or 1000 degrees Celsius! An electron beam is also a stronger energy source (due to a higher density), so generally it has better build rates and makes it possible to print with reactive and stronger materials. Some researchers have developed ways to produce parts from copper, niobium and bulk metallic glass on EBM printers.
Binder Jetting and Color Jet Printing
While some manufacturers focused on improving the heat source to melt powder better, others chose to improve the SLS method another way. Binder jetting technology also prints with powder (gypsum, sandstone, metal) but instead of sintering or melting it, these machines use an agent to bind grains together. Just imagine pouring glue on sand – this machine does almost the same thing but with extremely thin layers and under precise computer control. The process starts the same: a roller puts a thin layer of powder material across the build area. Then the 3D printer applies a binder agent to the areas, which should be connected. After that the platform goes down and a new powder layer comes on board to continue on the next layer.
On top of that, the gluing agent can be combined with color inks – in this case it’s possible to print a colored object within 390,000 combinations of CMYK colors from sandstone. This method is called Color Jet Printing (CJP) and it’s popular among artists and architects.
- Advantages: Requires less energy than SLS; can print beautifully colored prints; doesn’t require supports and can print same geometries as SLS printers
- Disadvantages: Objects are fragile and require coating to prevent absorption of moisture from the air; can’t produce hollow enclosed parts
Multi Jet Fusion (MJF)
MJF technology is quite young in comparison to previously mentioned technologies above. If explained simply, MJF is like a hybrid between Binder Jetting and Laser Sintering. As is the case with both of them, MJF works with a certain powdered material to create an object - PA 12 (Polyamide). Printing starts with jetting a fusing agent and a detailing agent onto the areas mapped out by the code. This melts powder grains, and then the printing continues with heating the powder by a lamp after every single layer created.
- Advantages: Several times faster printing; smooth surface; prints can go through different post-processes (coating, varnishing, sandblasting, painting)
- Disadvantages: Currently it’s possible to print with polyamide only; rare and expensive technology; hollow and enclosed objects are still impossible
Material Jetting (MJP, MJF and PolyJet)
Material jetting 3D printing technology is a method most commonly compared with 2D printing with inks. Like FDM, this technology spreads the material on a build platform. However, instead of melting a solid material, it works with liquid photopolymers which are cured by UV-light after a single layer is applied. Also, the difference is that instead of using a nozzle that moves across the printer, some material jetting machines have several nozzles to allow for some industrial printers to combine several materials at the same time. Range of photopolymers available is excellent – it’s possible to print flexible, tough, colored and biocompatible parts.
- Advantages: High resolution prints (up to 16 microns); smooth surface; complex geometries which require supports can be printed with a different support material for easy removal
- Disadvantages: parts change properties overtime when exposed to light and heat
Laminated Object Manufacturing (LOM or Selective Deposition Lamination)
LOM 3D printers are probably the most similar to their 2D predecessors which print documents and photos on paper. That’s because this technology works with sheets of adhesive-coated material (paper, plastic or metal). LOM printing starts with bringing a first sheet to a build platform, where a knife or a laser cuts a form of an object according to the code. After a layer is completed, a new sheet of material is applied to the platform. Then the platform glues and presses the sheets together and starts cutting a new form. This process continues for every layer until a final part is produced in its entirety. A printed piece needs to be removed from extra material after printing. LOM printing can be colourful, too, with impressive precision. Even if an object had been printed using an ordinary copy paper, it’s quite solid and can even be drilled! That makes LOM technology one of the cheapest and environmentally friendly options available. Paper prints display wood-like properties and can be strengthened through post-processing.
- Advantages: Materials can be cheap and accessible as well as fully recyclable; full-color printing is available with 360° HD color accuracy in over 1 million different shades; capable of printing large parts
- Disadvantages: Dimensional accuracy is lower compared with SLA and SLS printing; printed parts are far away from end-use parts
One more technology, which allows playing with CMYK inks, appeared recently on the market when company XYZ Printing released their da Vinci Color machine. Inkjet FDM printing is a mixture of single-nozzle FDM printing and ink jetting. The printer builds an object layer-by-layer by melting a string of white plastic but with a kicker, it adds ink at every layer. As a result, Inkjet FDM printers are capable of producing parts in a multitude of colors like that of industrial machines but within a desktop format.
- Advantages: Millions of colors available
- Disadvantages: Limitations and accuracy are still like an FDM printer; currently only one machine of this type on the market
3D printing is developing at a rapid pace, with new machines, upgrades, materials, software, and technologies appearing on the market every day. Some methods prove to be useful and become adopted into mainstream while others just copy previous techniques.
Learn more about 3D printing machines and their specifications in the 3D printers guide.